While drilling a wellbore in subsurface formations it is advantageous for measurement and command information to be transferred between the surface and the drilling tools in a timely fashion. Some drilling systems employ a high-speed communication network including communication media embedded in the drill pipe to facilitate timely information transfer between surface and downhole systems. Such drill pipe, known as “wired drill pipe” (WDP), includes communicative couplers at each end of each pipe joint and the aforementioned communication media extending between the couplers.
A system employing WDP for communication may include hundreds of individual wired drill pipes connected in series. Repeater subs may be interspersed among the WDPs to extend communication range. If one WDP (or repeater sub) has an electrical fault, then the entire communication system may fail.
In one particularly problematic scenario, an intermittent fault occurs while drilling, but disappears as the drill string is removed from the borehole. Such intermittent faults may be due to downhole pressures, downhole temperatures, shocks, rotating and bending, or other environmental effects that are not present when the drill pipe is retracted from the wellbore. If the fault cannot be traced to within a few joints of WDP, then large sections of WDP may have to be replaced. For example, if the repeater subs are spaced apart by 500 meters, then an intermittent fault may only be locatable to within the 500 meter section below the lowest repeater sub known to be operational. This uncertainty in the location of the fault may require large numbers of WDP joints to be available on the drilling rig. Each failure might require 500 meters of drill pipe to be replaced. If the fault only occurs under drilling conditions, then it may be impossible to identify exactly which drill pipe is failing at the rig site. Therefore, it is desirable to locate an intermittent fault while drilling, that is—while the WDP is in the borehole.